Questions

The Ryotwari system was introduced by  Sir  Thomas  Munro and   Captain   Alexander   Read   in 1820.This system  was in operation for  nearly  30  years  and  had  many features  of  revenue  system  of  the Mughals,    Under    the    Ryotwari System  every  registered  holder  of land is recognised as its proprietor and pays direct to Government

The error lies in the first part of the sentence. After superlative adjectives, majorly two prepositions are used: of and in. We use in with a singular word referring to a place or group. Eg: I am the happiest woman in the world. We use of before plurals, before time periods such as year/month. Eg: Sunday is the best day of the week. Here, in this case, the subject is the 'school', thus, it should be 'in the school'.

Calcitonin is 32-amino acid linear polypeptide hormone that is produced in humans primarily by the parafollicular cells of the thyroid, and in many other animals in the ultimopharyngeal body. It acts to reduce blood calcium, opposing the effects of parathyroid hormone.